This invention relates to foam formulations having blast-suppressant/containment capabilities.
Improvised explosive devices(IEDs) represent an increasingly dangerous threat to society, particularly when they contain a toxic chemical/biological (CB) agent. It is vital that both the blast effects pressure wave, heat and shrapnel) and the CB agent-containing aerosols resulting from the initiation of such devices are contained. CB agents also present a decontamination problem when deposited on the surfaces of various equipment and vehicles, or spilled on the ground.
In the last decade, there have been numerous patents and papers on the use of foam for blast suppression. For example, Clark described in his U.S. Pat. Nos. 4,541,947 and 4,589,341, an improved method for blast suppression through the use of fire fighting foams confined in a tubular barrier. Typically, the foams have an expansion 50:1-1000:1 and there is no mention as to its composition. The key to this invention is the methodology for containing the foam in a desired location.
U.S. Pat. No. 4,964,329 assigned to Broken Hill Ltd. describes a composition consisting of a mixture of foamable liquid and a particulate additive to be supported as a dispersion in the foam. The dispersion is claimed to be effective in sound attenuation and shock wave dispersion.
U.S. Pat. No. 4,442,018 of P. Rand describes a foaming composition useful for blast suppression: Such composition comprises a combination of water soluble polymer of the polyacrylic acid type, a foam stabilizer of dodecyl alcohol, a surfactant, a solvent.
A very interesting U.S. Pat. No. 5,434,192 describes a composition of surfactants and stabilizers consisting of a mixture of modified natural and synthetic polymer and solvents capable of producing foam viable for 12 hours to several stays at 75-105 degrees F. Such foam is used to suppress the emission of volatile gases and vapours.
A number of containment options are available. Initially, we conducted blast tests with a foam product called AFFF contained in nylon dome tents that were disposed over the threat. The results were very inconsistent; the foam would break down very quickly, it varied from a watery form to very light and airy. The lessons learned during this phase included the realization that the physical form of the foam could be varied considerably by flow rate, percentage of surfactant and nozzle adjustment. This work led to the development of the containment system is described in Applicant""s co-pending U.S. application Serial No. 60/069,533, filed. Dec. 12, 1997. That system includes a tent-like enclosure that is disposed over an TED and filled with an air-aspirated aqueous foam material which we have called Dispersal Suppressant Foam(DSF). The IED is then detonated, and the resulting shrapnel is contained within the enclosure. At that time, the foam material we used was a product sold under the trademark of SILVEX. Its formulation is covered by U.S. Pat. No. 4,770,794, which issued on Sep. 13 1988.
According to one aspect of the invention, a foam-forming composition having blast suppressant capability is provided, comprising (a) a surfactant 40-80%/w; (b) a foam stabilizer 0-7%/w; (c) a polyalkyleneglycol 10-30%/w; and (d) water balance to 100%.
In one embodiment of the invention, the polyalkylene glycol has the chemical formula R1xe2x80x94(OCH(CH3)CH2)nxe2x80x94OR2, where R1 and R2 are independently H, an alkyl, or an ester group and n greater than 1. The alkyl group may consist of a methyl, ethyl, propyl, butyl or a mixture thereof. In one example, R1 or R2 is hydrogen. In another example, both R1 and R2 are hydrogens.
Alternatively, the polypropylene glycol is a partially etherified polypropylene glycol derivative having the same formula R1xe2x80x94(OCH(CH3)CH2)nxe2x80x94OR2, but where only one of R1 or R2 is independently H, or an alkyl group and n greater than 1. Again the alkyl group representing R1 or R2 may be a methyl, ethyl, propyl, butyl group or a mixture thereof.
In one embodiment, the surfactant comprises a composition of either the formula [R(OCH2CH2[0])nX]aMb, where R is an alkyl group having from eight to eighteen carbon atoms[,]; n is an integer from 1 to 10; X is selected from the group of SO32xe2x88x92, SO42xe2x88x92, CO32xe2x88x92 and PO43xe2x88x92[:]; M is an alkali metal, alkaline earth metal ammonium or amine derivative; a is the valence of M and b is the valence of [R(OCH2CH2)nX], or[,] the formula [Rxe2x80x94CHxe2x95x90CH(CH2)mxe2x88x92X]aMb2 where R is an alkyl group having from eight to eighteen carbon atoms; m is an integer from 0 to 3; X is selected from the group of SO32xe2x88x92, SO42xe2x88x92, CO32xe2x88x92 and PO43xe2x88x92[,]; M is an alkali metal, alkaline earth metal, ammonium or amine derivative; a is the valence of M and b is the valence of [Rxe2x80x94CHxe2x95x90CH(CH2)mxe2x88x92X]a or a mixture thereof.